1. Field of the Invention
This invention relates to small size zoom lenses, and more particularly to small size zoom lenses of shortened total length (the distance from the front vertex to the image surface) suited for leaf shutter type cameras and video cameras.
2. Description of the Prior Art
The recent trend of minimizing the bulk and size of cameras such as leaf shutter type cameras and video cameras, has created the need for shortening the total length of the objective lens in these cameras. Also, a demand has grown for zoom lenses even on small cameras whose lenses are not interchangeable, or on leaf shutter type cameras. Such a zoom lens is necessarily as short in total length as conventionally employed fixed focal length lenses.
Many zoom lenses have been proposed which include the standard angle of view used widely in the ordinary leaf shutter type cameras (in terms of the 35 mm still camera, the total angular field of view 2w=47.degree. for a focal length of about f=50 mm), for example, in Japanese Patent Publication No. SHO 49-29146, a zoom lens includes two lens groups. Counting from the front, the first lens group is of negative refractive power and the second is of positive refractive power. The separation between the two lens groups is variable to change the magnification. Because the refractive power arrangement is in the order of negative and positive, the back-focal distance is long, which is advantageous in a single lens reflex camera, but tends to make the total length of the lens too long in leaf shutter type cameras.
The present applicant has previously proposed a zoom lens whose front and rear lens groups are of positive and negative refractive powers, respectively, and are movable in differential relation to effect zooming, as set forth in Japanese Laid-Open Application No. SHO 56-128911 corresponding to U.S. patent application Ser. No. 243,209, filed Mar. 12, 1981 now abandoned, and in Japanese Laid-Open Patent Application No. SHO 57-201213. As disclosed in these patent applications, the use of a new refractive power arrangement of positive and negative from the front to rear, provides the possibility of shortening the back-focal distance and achieving a zoom lens of shortened total length.